The present invention relates to a method for operating a hybrid motor vehicle.
German patent document DE 40 40 310 A1 discloses a method for operating a hybrid motor vehicle, in which the vehicle is operated exclusively by an electric motor during the start-up period of the vehicle. During start-up operation of the internal combustion engine of the vehicle, the part of the system that is connected upstream of the internal combustion engine is heated up to the operating temperature in order to guarantee a combustion with the lowest possible emission of harmful substances. After a warming-up phase, the electric engine drive is switched automatically and smoothly to an internal combustion engine drive within a very short period of time. Such a method requires electric energy to drive the vehicle in the start-up phase and to warm up the system components of the internal combustion engine. Thus, a significantly higher demand for electric energy is necessary over a longer period of time. In order to provide this higher amount of energy, as compared to conventional vehicles which are operated exclusively by an internal combustion engine, a larger energy accumulator is needed.
German patent document DE 44 22 647 A1 discloses a method for operating a hybrid vehicle, in which the required propulsion power is supplied primarily by an internal combustion engine. A portion of the required propulsion power may be supplied by an electric machine only in the event that the electric energy accumulator exhibits a sufficient charge.
The present invention provides a method for operating a motor vehicle that guarantees the lowest possible emission of harmful substances within a very short period of time. Since the torque required to drive a motor vehicle is divided as a function of the operating parameters, the fastest possible warming-up of the internal combustion engine may be guaranteed.
Below a specified threshold temperature of the internal combustion engine, the torque for driving the vehicle may be generated exclusively by the internal combustion engine. During this period of time, the electric machine may be driven by the internal combustion engine as an additional load. Therefore, the electric machine operates in a generator mode and feeds the generated electric energy into either an electric energy accumulator or a heat exchanger. The heat exchanger is heat-coupled with the internal combustion engine or proportionately into both and/or all electric consumers to be supplied with energy if desired, in addition to the energy accumulator or heat exchanger. Due to the specific additional load on the internal combustion engine, the internal combustion engine reaches a state, which exhibits an operating temperature that is optimal for burning harmful substances, within a very short period of time.
In an exemplary embodiment, the present invention provides not only the temperature of the internal combustion engine, but also the temperature of the electric machine, the temperature of the electric storage means, the rotational speed of the internal combustion engine and/or the rotational speed of the electric machine as the operating parameters, according to which the torque is divided. The operating parameters may be recorded either by measuring techniques or may be determined arithmetically with models that are stored and map the corresponding processes.
A capacitor assembly may be used in an advantageous manner as the electric accumulator. For example, high power capacitors known as “supercaps,” may be used. Supercaps can supply a large amount of energy for a short period of time. Supercaps are superior to conventional batteries, because supercaps can be re-charged in a very short period of time (and are, therefore, ready again for use). Hence, supercaps may be charged up by the electric machine, which is driven in the generator mode by the internal combustion engine, and/or by recuperation during the braking operation within a very short period of time.
In another exemplary embodiment of the invention, not only the lower threshold temperature of the internal combustion engine, but also an upper threshold temperature of the internal combustion engine is determined. Below the lower threshold temperature, the hybrid vehicle is operated exclusively by the internal combustion engine. After reaching the lower threshold temperature and up to the upper threshold temperature in a mixed operation, the hybrid vehicle is operated proportionately by the internal combustion engine and by the electric machine as a function of the parameters. Above the upper threshold temperature (as far as this is possible with just the electric machine), the hybrid vehicle is operated exclusively by the electric machine. The threshold temperature values can be modified as a function of the other operating parameters (see description with respect to FIG. 2).
In accordance with exemplary embodiments of the present invention, the internal combustion engine is converted from a cold operating state (load point increase below a first threshold temperature) into a warm operating state with optimal combustion properties within a very short period of time. Furthermore, within the warm operating state of the internal combustion engine, the vehicle may be driven either partially by the electric machine (decrease in the load point above the first threshold temperature) or entirely by the electric machine alone (above a second threshold temperature). Above the second threshold temperature, the torque required by a driver's request may be converted by the electric machine alone to the extent that this torque can be generated by the electric machine. If the requested torque is so large that it cannot be converted by the electric machine alone, the internal combustion engine is switched on, at least temporarily, proportionately by way of the coupling for the purpose of generating the differential torque.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.